Let's take
4x + y + 5z = -40 (Eq1)
-3x + 2y + 4z = 10 (Eq2)
x - y - 2z = -2 (Eq3)
Now create a new system using elimination
-2* (4x + y + 5z = -40) (Eq1)
1* (-3x + 2y + 4z = 10) (Eq2)
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-11x - 6z = 90 (Eq4)
Use elimination again
1* (-3x + 2y + 4z = 10) (Eq2)
2* (x - y - 2z = -2) (Eq3)
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-x = 6 (Eq5)
From Equation 5 we have that
x = -6
Replace the value of x in Equation 4 and clear z
-11(-6) - 6z = 90
-6z = 90 - 66
-6z=24
z = 24/-6
z = -4
Replace x and z in equation 3 and clear y
-6 - y - 2*(-4) = -2
-y + 8= -2 +6
-y = 4 - 8
-y= -4
y = 4
